Method and apparatus for producing an electrical connection with insulated wires



Nov. 19, 1963 cs. N HARRIS 3,111,554

METHOD AND APPARATUS FOR PRODUCING AN ELECTRICAL CONNECTION WITHINSULATED WIRES Original Filed June 5, 1956 C C g GEORGE N.HARR|S ii-hINVENTOR.

1-- -I 40' 4 I a hmq 1% 3,111,554 Patented Nov. 19, 1963 ice 3,111,554METHOD AND APPARATUS FOR PRODUCING AN ELECTRICAL CONNECTION WITHINSULATED WIRES George N. Harris, Madison, Wis., assignor to AMPIncorporated, Harrisburg, Pa. of application Ser. N 589,544, June 5, 30,1962., Ser. No.

Continuation 1956. This application Oct.

6 Claims. (11. 174-84) This invention relates to electrical connectorsof the type adapted to join together one or more wires or conductors bypressure forming and more particularly to a pressure formed electricalconnector of the type adapted to join wires coated with tough filminsulations.

Many wires commonly used in the electrical industry and which must bejoined together are coated with a tough film insulation such as enamel,polyvinyl acetal and the like. In addition many wires become dirty anddevelop corrosion or oxide layers which act as insulation. Obviously tomake a good low resistance connection with such wires these insulatinglayers must be removed.

Heretofore various connectors and methods of forming them aboutconductors have been proposed including sharp piercing teeth topenetrate the insulation, scraping of the insulating coating beforeconnection, partially shearing of the conductors to expose virgin metaland the like. These have included some connectors and crimps that havebeen successful for limited ranges of wire sizes and types.

According to the present invention I have provided an improved connectorand method of applying same which provides improved electrical andmechanical properties over a Wider range of wire and connector sizes andcombinations thereof than heretofore known. Briefly I accomplished thisby rupturing the insulating film and then causing it to be movedlongitudinally from a portion of the wire to expose a greatly increasedarea of bare metal to provide improved low resistance contact throughthe connection.

Accordingly it is an object of the present invention to provide animproved crimp for an electrical connector that will make contactthrough the toughest film type insulation coatings over a wide range ofWire sizes without destroying the mechanical strength of a connectionmade therewith. It is another object of the present invention to providea crimp for an electrical connector of the solderless type for joiningtogether wires coated with tough insulating films that will expose anincreased area of low resistance electrical contact between connectorand wires without mechanically weakening the wires. It is another objectof the present invention to provide a crimp for a solderless connectorfor joining wires coated with enamel, polyvinyl acetal and similarcoating that has improved tensile strength, bend and securcnessperformance. It is another object of the present invention to provide anelectrical connector which gives a greater area of stripped wire and amore positive contact therewith. It is a still further object to providean electrical connector that will provide an increased area of virginmetal contact at a larger cross-sectional area point of the conductorsbeing joined than heretofore possible. These and other and furtherobjects will be in part apparent and in part pointed out as thespecification proceeds.

In the drawings:

FIGURE 1 is a perspective view of a connector and connection accordingto the present invention showing a solid copper wire being joined to astranded conductor;

FIGURE. 2 is a view similar to FIGURE 1 showing the reverse side of theconnector of FIGURE 1;

FIGURE 3 is a longitudinal sectional view of the con ncction of FIGURE1;

FIGURE 4 is a diagrammatic view in exaggerated scale showing thepiercing burrs on the edges of the serrations;

FIGURE 5 is a longitudinal sectional view through the crimping dies ofthe present invention;

FIGURE 6 is a cross-sectional view of the dies of FIGURE 5; and

FIGURE 7 is a cross-sectional view similar to FIG- URE 3 showing anotherembodiment of the present invention.

This application is a continuation of my prior copcnding application,Serial No. 589,544, filed June 5, 1956, now abandoned.

Referring now to FIGURES l and 2 a connector 10 according to the presentinvention is shown orimped about the stranded wires 12 of an insulatedcable 14 and a solid wire 16 insulated with a tough film insulation suchas enamel, polyvinyl acetal or similar substance. In the embodimentshown in the present invention no contact or tongue portion is shown forthe connector 10 but it is obvious that the present invention isapplicable to connectors having as a part thereof one of the variouscontact portions adapted for attachment to another conductor, bindingpost or terminal device. Similanly while the solid wire 16 is shown asthe one being covered with the film insulation 18 the strands of Wire 12might similarly be insulated (eg. acetate wound stranded DeltahcstonRange Wire) and a good connection still obtained. The connector 10 isgenerally made of a metal such as brass, Phosphor bronze, nickel platedsteel and the like which is relatively harder than the conductor metalwhich is usually copper or a soft aluminum.

Referring now to FIGURE 3 the tough insulation film 18 is shown as aheavy line on the surface of the solid wire 16. The connector is shownas carrying therein a number of grooves or serrations 20 which extendtransversely across the barrel portion of the connector and are locatedabout the mid point of the connector 10. The grooves 20 are shownextending across the bottom (FIGURE 3) of the connector and part way upthe side walls thereof. In certain applications these grooves may extendthroughout the entire width of the connector particularly where twosolid wires insulated with Formvar or the like are to be joined.

The grooves or serrations 20 are advantageously of smaller width thanthe diameter of the Wire 16 although generally they are of greater widththan the diameter of the strands of the cable 14. In FIGURE 4 it will beseen that when the grooves 20 are formed in the connector 10 the edges36 are actually raised a little bit to form sharp projections or burrsthat aid in the penetration of the insulation film 18. Also the sidesare tapered to give an improved contact action as described and claimedin the copending application, Serial Number 361,205, filed June 12,1953, to Kemper M. Hammell, now US. Patent No. 2,800,638, issued July23, 1957. The serrations 20 are shown as having a depth greater than thethickness of the film 18 and less than the diameter of the wire to becrimped, however this is not always necessary for a successfulconnection. Also it should be noted that the grooves or serrations 20may vary in depth from the bottom where they contact wire 16 and the topwhere they contact the strands of cable 14. Naturally the depth would beless at the top so as not to completely sever the smaller strands ofcable 14. As may be seen in FIGURE 3 the grooves 20 are well spaced toprovide substantial land areas for good mechanical contact while stillproviding sufficient shearing edges for good electrical contact. Detailsas to the desired spacing, depth, width, and so on of the grooves forvarying wire sizes are discussed in the 3 above Hammell application andare not repeated here for the sake of brevity.

Turning now to FIGURES 2, 5 and 6 it will be seen that the anvil portion24 of the die assembly 26 has a generally concave face with longitudinalfiat edges and a raised central portion 28. Die 26 tapers from portion28 toward each edge thereof. This taper is equal on both sides and formsenlarged ends on the connector providing a gradually tightening grip onthe wire as it enters the connector. A taper angle of about six degreeshas been found to be advantageous and helps to give an accentuatedextrusion as will be described herein.

FIGURE 5 shows the face portion 28 of the anvil extending through thecentral serration area of the connector and the tapered portions 30extending outwardly to the ends of the connector 10. The other die 32overhangs the left end of the connector FIGURE 5 (with rounded cornersto avoid nicking the wire) but is overhung by the connector on the rightend to provide a portion of the connector accessible for stripping.

In the actual crimping operation as the dies force the connector intocontact with the wires therein the burrs 36 rupture the insulation film18 at the points shown by the arrows in FIGURE 4 deforming the burrs inthe process. Additional pressure on the connector causes the conductor16 to bend down into the serrations 20. Next the conductor surfacestarts to shear at the points of the arrows in FIGURE 4 and a ring ofinsulating coating and wire is forced down toward the bottom of theserrations. At the center serration this process continues until thering of insulating coating rests in the bottom of the serration andfreshly sheared virgin conductor surfaces are wedged, by virtue of thetapered side walls of the grooves as described above, into the serrationto make good electrical contact with the edges thereof.

Continued pressure from the dies on the connector 10 starts to cause thewire 16 to extrude longitudinally from between the dies in the centersection corresponding to the face 28. This conductor motion isaccentuated by the double tapered anvil 24 and, aided by the differencein hardness of the metals, is greater than the motion of the adjacentmetal in the connector 10. The motion of the conductor carries with itthe insulating coating 18 which starts to expose additional areas oneither side of the central serration as indicated at 38. This slidingcauses the insulation to slide over the inner edge of the outerserrations and down into the bottom thereof. This covers the inner edgeand bottom of the outer serration but is stopped at the outer edgethereof. Also at the outer edge of the outer serrations this slidingcauses the insulation to flow outwardly from the burrs at the edge ofthe serrations. This flow, accentuated by the double taper anvil asmentioned above, causes an increasingly larger annular ring to beexposed outwardly of the greatest amount of crimping indentation asindicated at 40. As may be seen in FIGURE 2 this pressure formingresults in a flat impression in the bottom of connector 10 whichcoincides with the area of maximum reduction in cross-sectional area andtapered portions 22 of progressively lesser reductions which graduallyrelieve the pressure outwardly to the edge of the connector. Thischanging reduction of cross-sectional area helps produce an accentuatedextrusion of wire 16 causing a large relative movement thereof past theserrations which scrapes and moves the insulating layer 18 from a large,at least semi annular area adjacent the edge of the serrations.

As can be readily seen the cross-sectional area of the wire 16 has notbeen reduced as much at areas 40 as it has at the areas 38 for instance,and thus there is provided a path of reduced resistance from theuncrirnped wire through the area 40 into the connector 10, which haslarge current carrying capacity and low resistance. Thus the currentflows from the wire 16 through the connector 10 and thence to the cable14 reducing the millivolt drop in the splice connection and in turnreducing the temperature rise encountered in the usual connection ofthis type.

Since the major portion of the low resistance contact area is uncoveredby the relative sliding of the insulated solid wire after rupture of theinsulation and the connector 10 the serrations or grooves 20 need not heas deep as where the electrical contact must be obtained by the exposureof sheared surfaces as by partially shearing the wire. This togetherwith the double tapered effect gives a much stronger mechanicalconnection and electrical conductivity.

Referring now to FIGURE 7 there is shown another embodiment of thepresent invention wherein the com nector 10' has only one tapered area22' and a flat central area. A plurality of grooves 20 are provided onthe inner surface of connector 10 as in the embodiment of FIGURE 3 andin addition they extend down into the tapered area 22'.

The crimping dies for the embodiment of FIGURE 7 are the same as forFIGURE 3 except that the taper 30 is omitted from one end. The flatportion is impressed the deepest to cause the serrations 20' to rupturethe coating 18 and extrude the conductor 16' longitudinally from withinthe connector 10'.

A similar separating action occurs at the edge of the serrations 20 asin the previous embodiment with the largest exposure of virgin metaloccurring at the outer edge of a serration intermediate the fiat portionand the end of the tapered portion 22'.

It is thus apparent that I have provided an improved connector andmethod of connecting conductors, at least some of which are coated withtough enamel, polyvinyl acetal and similar film type insulations,resulting in both improved electrical and mechanical characteristics forthe connection.

While there is given above a certain specific example of this inventionand its application in practical use, it should be understood that thisis not intended to be exhaustive or to be limiting of the invention. Onthe contrary, this illustration and explanation herein are given inorder to acquaint others skilled in the art with this invention and theprincipals thereof and a suitable manner of its application in practicaluse, so that others skilled in the art may be enabled to modify theinvention and to adapt and apply it in numerous forms each as may bebest suited to the requirement of a particular use.

I claim:

1. A crimp for an electrical connector of the type adapted to join oneor more electrical conductors together by pressure forming whichcomprises in combination with at least one wire coated with a toughinsulating film and an electrical connector of a harder metal than theconductors and having a plurality of transverse grooves therein formedthereabout, a transverse imp-ression located about the mid point of theconnector bottom, a taper portion at each end of said impressiongradually releasing the pressure from said impression outwardly to theedge of said connector, and said impression and taper portions having aconvex outer surface forming the bottom of said connector.

2. A crimp for a sheet metal electrical connector of the type having abarrel portion carrying therein a plurality of transverse serrationsadapted to be curled up around a plurality of conductors coated with atough insulating film comprising a smoothly curving upper portion coinedinto intimate contact with the conductors therein and a bottom portiontapering from one end of the barrel to the other from a maximum coiningof the conductors therein to substantially no coining thereof wherebysaid serrations will require the insulating film and said bottom taperwill accentuate the extrusion of the conductors to expose substantialareas of bare condoctor to intimate contact with the connector, theconnector being of harder metal than the conductors.

3. In an electrical connection joining a conductor coated with a filminsulation to a connector, a metallic connector barrel disposed aroundsaid conductor and having a plurality of substantially transverseserrations between substantial land areas on a surface thereof, theedges of said serrations being sharp and breaching said insulation alongtransverse lines, a major portion of said barrel being compressed insubstantially uniformly increasing tightness relative to the length ofsaid conductor to provide an accentuated extrusion of the conductor inthe direction of decreasing tightness, and a plurality of gaps in saidinsulation exposing bare wire for contact with surfaces of said barreladjacent said serrations, said gaps being respectively defined betweenan edge of said serrations and the limit of conductor extrusion relativeto said edge.

4. The method of crimping a conductor having a tough resilient film-typeinsulation in a harder metal connector having transverse sharp-edgedgrooves which includes the steps of disposing the conductor in theconnector to lie across the grooves, reducing the connectorcross-section to bring the groove edges into cutting relation with theconductor insulation, pressure-forging a first portion of the connectorinclusive of at least some of the grooves with sufficient pressure tosubstantially reduce the cross-sectional area of and to extrude theconductor and the insulation longitudinally outward from the centerthereof while simultaneously pressure-forging the remaining connectorportions with a progressively decreasing pressure away from the firstportion, the grooves and the outer edges thereof relative to the centerof the first portion presenting barriers to outward movement ofinsulation so that substantial areas of bare conductor for contact withthe connector are exposed adjacent the outer edges upon extrusion of theconductor and insulation outwardly therefrom.

5. The method of crimping a conductor having a tough resilient film-typeinsulation in a harder metal connector having transverse sharp-edgedgrooves which includes the steps of disposing the conductor in theconnector to lie across the grooves, reducing the connectorcross-section to bring the groove edges into cutting relation with theconductor insulation, cylindrically pressure-forging a portion of theconnector inclusive of some of the grooves with sufficient pressure tosubstantially reduce the crossscctional area of and to extrude theconductor and the insulation longitudinally outward in either directionfrom the center thereof will simultaneously pressure-forging theremaining connector portions with a progressively decreasing pressureaway from the cylindrical portion, the grooves and the outer edgesthereof relative to the center of the cylindrical portion presentingbarriers to outward movement of insulation so that substantial areas ofbare conductor for contact with the connector are exposed adjacent theouter edges upon extrusion of the conductor and insulation outwardlytherefrom.

6. The method of crimping a conductor having a tough resilient film-typeinsulation in a harder metal connector having transverse sharp-edgedgrooves which in eludes the steps of disposing the conductor in theconnector to lie across the grooves, reducing the connectorcross-section to bring the groove edges into cutting relation with theconductor insulation, pressure-forging a first portion of the connectorinclusive of at least some of the grooves with sufficient pressure tosubstantially reduce the crosssectional area of and to extrude theconductor and the insulation longitudinally outward from. the centerthereof, and pressure-forging the remaining connector portions inclusiveof the remaining grooves with a continuously progressive compressionaway from the first portion to cause a differential pressure to progressalong the length of the connector for accenturating the extrusion of theconductor and insulation in the direction of the progressivecompression, the grooves and the outer edges thereof relative to thecenter of the first portion presenting barriers to outward movement ofinsulation so that substantial areas of bare conductor are exposed incontact with the lands between the grooves of the connector adjacent theouter edges upon extrusion of the conductor an insulation outwardlytherefrom.

References Cited in the file of this patent UNITED STATES PATENTS2,622,314 Bergan Dec. 23, 1952 2,692,422 Pierce Oct. 26, 1954 2,800,638Hammell July 23, 1957 2,802,257 Hotzapple Aug. 13, 1957 FOREIGN PATENTS573,920 Great Britain Dec. 12, 1954

1. A CRIMP FOR AN ELECTRICAL CONNECTOR OF THE TYPE ADAPTED TO JOIN ONEOR MORE ELECTRICAL CONDUCTORS TOGETHER BY PRESSURE FORMING WHICHCOMPRISES IN COMBINATION WITH AT LEAST ONE WIRE COATED WITH A TOUGHINSULATING FILM AND AN ELECTRICAL CONNECTOR OF A HARDER METAL THAN THECONDUCTORS AND HAVING A PLURALITY OF TRANSVERSE GROOVES THEREIN FORMEDTHEREABOUT, A TRANSVERSE IMPRESSION LOCATED ABOUT THE MID POINT OF THECONNECTOR BOTTOM, A TAPER PORTION AT EACH END OF SAID IMPRESSIONGRADUALLY RELEASING THE PRESSURE FROM SAID IMPRESSION OUTWARDLY TO THEEDGE OF SAID CONNECTOR, AND SAID IMPRESSION AND TAPER PORTIONS HAVING ACONVEX OUTER SURFACE FORMING THE BOTTOM OF SAID CONDUCTOR.